Stamping and forming die assemblies of the type used in punch presses for carrying out operations on strip material frequently contain tool members which must move relative to the reciprocable ram in which they are carried while the ram is moving from its open position to its closed position, in other words, while the forming operations are being carried out on the strip material. For example, it is common practice to design a die assembly having a forming tool which is in an extended position during initial movement of the ram from its open towards its closed position so that the tool can perform a forming operation on the strip material. At an intermediate stage of the stroke of the ram, it is then necessary that the forming tool remain stationary while the ram continues its movement to its closed position. It is common practice to provide heavy duty springs on the forming tool which are overcome by the ram when the forming tool stops moving so that the spring is compressed during the final portion of the stroke of the ram. When the ram returns to its open position, the compressed spring returns the forming tool to its extended position.
While the use of compression springs to achieve the overtravel of the ram relative to the forming tool has been used with satisfactory results in many die assemblies, the use of springs does have certain disadvantages. For example, the springs must be capable of withstanding a very large number of cycles and must be, in many cases, extremely stiff. The springs, therefore, must be relatively large relative to the size of the tool itself. The springs undergo fatigue in time and fail so that they must be replaced. Also, the use of springs necessitates the use of a relatively high capacity press for the reason that the energy required to compress the springs is in addition to the energy required to carry out the stamping and forming operations which are performed on the strip material.
The present invention is directed to the achievement of mechanisms for controlling the movement of tooling in a die assembly which avoids the use of heavy duty springs. The invention is particularly directed to the achievement of a toggle mechanism by means of which the relative movement of the tooling member with respect to the press ram is positively controlled.
The embodiment of the invention described below is particularly intended for use in a stamping and forming machine having first and second ram assemblies which are movable relatively towards and away from each other during each operating cycle of the machine. Stamping and forming machines of this type are fully described in U.S. Pat. Nos. 4,497,196 and 4,819,476 which are hereby incorporated by reference into this description.